This invention relates to a simple, economical method of sizing the inside diameters of tubular valve guide inserts after the inserts are forced into the reamed valve guides.
The method of inserting phosphor bronze valve guide liners of one type to which the present invention relates is described in U.S. Pat. Nos. 3,828,415 and 3,828,756. The specifications and drawings of these patents are specifically incorporated herein by reference. Basically, the worn-out valve guides are rebuilt by reaming them so as to enlarge the diameters thereof. A tubular, longitudinal insert is forced into each of the reamed valve guides to provide a new surface for the valve stem. The inserts have a stepped longitudinal slit extending the length thereof. This slit closes as the insert is forced into and radially compressed by the reamed guide. The inserts, when in working position, have an outer diameter slightly greater than or equal to the inner diameter of the reamed guide and are retained in position by the radial compression of the guide. The inserts are also utilized in the manufacture of original equipment.
In typical internal combustion engine building or rebuilding operations, the insides of such tubular metal inserts, after insertion are finally sized with a reamer to insure concentricity and the desired clearance between the inner diameter of the inserts and the valve stems which will reciprocate therein. This is a labor-intenstive process requiring specially fluted, heat treated and ground reaming tools. It removes, moreover, the interior surface layer of the liner which, when the same is the product of a rolling operation as set forth in the aforementioned patents, is substantially harder and thus capable of longer wear than the adjacent liner metal.
Instead of using the rolled liners which are the subject of the aforementioned patents, machined cylindrical bronze inserts, knurled or otherwise, may be utilized. A third alternative is to merely knurl the interior of the worn cast iron guide to displace metal inwardly. It remains generally necessary, in either of these cases, to finally size the guide inner diameter with a reamer or like cutting tool. The final sizing process does nothing to burnish or harden the working surface of the guide. In the case of the knurled guide, it actually removes additional metal, further weakening the working area of the guide and wasting metal which could otherwise be usable in a subsequent rebuilding operation.
It has been proposed previously to substitute a broaching process for the reaming process to finally size the guides. The proposed tool consisted of a spherical broaching element on the end of a short rod. The sphere diameter corresponded to the desired diameter of the valve guide insert. At the other end of the rod was a female joint for receiving the male joint of a driver rod roughly the same diameter. In operation, the male-female joint frequently fractured when subjected to the hammering, particularly air hammering, required to drive the broaching ball element through the valve guide. Furthermore, many of the spherical elements were found to scrive or score the insides of the tubular valve guide rendering them either unfit for use or of marginal fitness for use.